In this paper the factors which influence the isolation and the insertion loss of optical circulator are discussed. Theoretically and experimently ther is an optimum chioce between absorption and polarization characteristics of polarizing prism for a polarization-incependent optical circulator with low insertion loss and high isolation. Experiment shows that the insertion loss of our circulator was about-1dB and the isolation was between - 25.5dB and - 28dB.